1. Field of the Invention
The present invention relates to a technology for compounding a LAN (Local Area Network) communication channel and other communication channels and, particularly, to a compound transmission system for compounding and transmitting signals of a LAN communication channel and other telephone communication channels or other data communication channels without using a frame or time-division multiplex technique.
2. Description of the Related Art
It has been usual that a LAN communication channel and a communication channel of another communication system are provided separately from each other. Recently, however, a technology by which a LAN signal on a LAN communication channel and a signal on a communication channel of another communication system are frame-multiplexed by using a time-division multiplex technique and transmitted through a single transmission path is becoming popular. For example, IEEE802.9 defines a technology for compounding communication channels of a LAN communication system and a telephone exchanger by using a time-division frame-multiplex.
Signals to be multiplexed by a multiplex communication device according to the IEEE802.9 definition have 2B+D+P frame structures and a LAN signal is transmitted in the P frame after converted into packet data and an exchange signal used for a communication of the telephone exchanger is transmitted in the B frame. Therefore, the exchanger requires a trunk dedicated to the 2B+D+P frame structure and the LAN communication system requires a special device referred to as "access unit" as an interface for a communication path of the 2B+D+P frame signal.
In the conventional multiplex communication device mentioned above, frame transforming adapters, for multiplexing the LAN signal from the LAN communication system and a communication signal from the exchanger by using the dedicated 2B+D+P frame structures, are required at a transmitting side. Also, at the receiving side, the dedicated frames received by the LAN communication system and the exchanger on the other side are demultiplexed by frame transforming adapters to recover the LAN signal and the telephone communication system. Therefore, the conventional multiplex transmission system is very expensive and, since the 2B+D+P frames dedicated to the respective LAN communication system and the exchanger are used, a maintenance of the communication system is difficult and there may be considerable communication delay.